1. Field of the Invention
The invention relates to a torsional vibration damper with a friction device for installation in a vehicular transmission.
2. Description of the Related Art
A torsional vibration damper for a vehicular transmission is known, for example, from DE 35 16 291 C2, which has a drive-side transmission element and an output-side transmission element that is rotatable relative to the drive-side transmission element, wherein each of the drive-side and output-side transmission elements comprises a centrifugal mass. A friction device which has two separate friction elements is operatively held between the transmission elements. A friction disk pressurized by an axial spring is operatively held between the transmission elements in their radial inner area. During any movement of the two transmission elements relative to each other, the friction disk produces a base friction effect of the device. Provided radially outside of this friction disk is an angled friction piece that axially penetrates one of the transmission elements with clearance in the circumferential direction. As the relative movement between the two transmission elements increases, the amount of clearance in the circumferential direction decreases. As soon as this clearance is used up, the angled friction piece acts in addition to the aforementioned friction disk, so that an additional load friction is added to the base friction effect.
This friction device makes it possible to counteract greater torsional vibrations with greater friction. However, because of the two separate friction elements, the device is relatively large and expensive. Furthermore, because the base friction effect is applied at all times, the load friction can only reinforce the base friction. The jump between the two levels of friction, especially using the materials which are normally used, is relatively large. Thus, no finely-graduated adjustment of the friction effect to particular operating conditions is possible and the vehicle in which this torsion damper is installed is driven with either too much or too little friction.
Another friction device between transmission elements that are movable relative to each other is described in DE 38 00 566 A1. This friction device has friction elements that are dependent on centrifugal force and thus on speed. Attached to one of the transmission elements is an angled friction piece. A counter friction element is urged into resting contact with a radially outer area of the angled friction piece. During increasing centrifugal force, the spring is compressed and the friction between the angled friction piece and the counter friction piece is thus reduced.
In prior art device having speed-dependent friction elements such as those described in the above prior art documents, the relatively high construction costs of these devices are accepted as a trade off for the advantageous results.